Having determined the structure of crystals of deoxy sickle cell hemoglobin (beta 6 glu yields val, one crystal form) and deoxy Hb C (beta 6 glu yields lys, two crystal forms) at 3 Angstron units resolution, it is proposed to refine these models so their calculated diffraction patterns best agree with those experimentally observed. After refinement the intermolecular contacts will be examined and cataloged. We have prepared crystals of deoxy Hb A, S, and C all in the same lattice and space group. It is proposed to determine the degree to which these crystals are isomorphous. The crystals of deoxy Hb C are resistant to X-ray damage, grow readily and diffract very well. It is proposed to work out their structure at a resolution better than 2.5 Angstron units. Hemoglobins Vancouver, Mobile and Korle Bu all are modified at beta 73 asp, a residue involved in the sickling reaction. It is proposed to determine the structures of these hemoglobins and to examine the intermolecular contacts in these crystals.